Fluid coking process



July 21, 1959 v w. H. JONES- ETAL 4.

FLUID coxmc; PROCESS Filed March 15. 1954 2 Sheets-Sheet 1 COK E come" ,29

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By )7": M Attorney July '21, 1959 w. H. JONES ETAL 2,8 5, 0

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WILLIAM H. JONES HOMER Z.MARTIN INVENTORS av M ;,,,7%..- ATToRnEY FLUID COKING PROCESS 'William H. Jones, Baton Rouge, La., and Homer Z.

Application March 15, 1954, Serial No. 416,210

3 Claims. (Cl. 208-=-l27) This invention relates to a fluid coking process and apparatus, and particularly to a scheme suitable for carrying out fluid coking on a commercial scale. Still more specifically it relates to a scheme for equalizing temperatures, and preventing stickiness and excessive agglomeration in tall fluid coking reactors. This application is a continuation in part of application entitled, Fluid Coking Process, Serial No. 388,474, filed on October 22, 1953, now abandoned, by William H. Jones and Homer Z. Martin, co-inventors of the invention disclosed and claimed in the present application.

Fluid coking is basically well known. It consists of introducing a heavy hydrocarbon feed such as petroleum pitch into a dense fluidized bed of finely divided solids at an appropriate coking temperature and at a total feed rate of about 0.3 to 2 or even 5 weight of liquid feed per hour per weight of fluidized solids. The fluidizing gas velocities usually range from about 0.5 to 3 ft./sec. The coking temperature may range from about 850 to 1500 F. or higher depending on the main object of the operation. Temperatures below about 1100 F. are preferred when it is desired to produce a maximum of distillate in the gas oil range for conversion into motor fuel by catalytic cracking, whereas temperatures above about 1200 F. are preferred when the main object is to make aromatic and olefinic hydrocarbons. In either case the hydrocarbon feed is generally introduced into the fluidized bed at a given level through a single nozzle or ring of nozzles and is pyrolytically decomposed in the reaction zone, forming the desired hydrocarbon vapors which are withdrawn for further processing, and a carbonaceous deposit which is laid down in film-like layers on the fluidized particles. Consequently, it is customary to Withdraw a portion of the solids from the reaction zone, in part to recover net product coke, in part to grind some of the coke for return to the reactor so as to maintain an approximately constant particle size distribution in the reactor, and in part to circulate some of the coke to .a heater where the circulating coke is heated and then returned to the coking reactor to supply the required heat of coking.

Such processes have been successfully demonstrated in the laboratory and in small pilot plants. However, despite extensive experience with fluid catalytic cracking reactors, unforeseen complications have been encountered in the operation of larger fluid coking reactors, particularly in those having a high ratio of height to diameter. As an example, a cylindrical coker of about 5000 bbl./day pitch feed capacity operating at a pitch feed rate of about 0.5 weight of pitch per hour per weight of fluidized solids in the reactor and at a gas velocity in the upper part of the vessel of about 3 ft./sec. will be about 9 feet in diameter and 75 feet high and contain a dense fluidized bed about 60 feet deep. Unlike conventional fiuid catalytic cracking units, such fluid coking reactors have the undesirable tendency of developing considerable and erratic temperature difler- 2,895,904 Patented July 21, 1 959 for the fluidized solids to get rather sticky and to cause bogging of the fluidized bed at pitch feed rates previously found satisfactory in pilot operations. Another symptom of unsatisfactory operation is the formation of large agglomerates, resulting in a loss of valuable seed coke.

It is an object of this invention to provide a fluid coking process and apparatus having improved temperature distribution characteristics, improved fluidization characteristics at satisfactory hydrocarbon feed rates, and reduced tendencies toward particle agglomeration, especially in tall reactors having a ratio of height to diameter of at least 6 to 1 and notably as high as 10 or 20 to 1. Another object is to present a scheme for injecting a heavy hydrocarbon oil feed into a fluid coking vessel regardless of the vessels shape whereby bog- .ging and caking of the fluidized solids bed is avoided. These and other objects, as well as the general nature and advantages of the invention and the best mode presently contemplated for carrying it out will be made apparent in the following description and accompanying drawing.

The drawings, forming a part of this specification, are schematic illustrations of apparatus embodying the present invention and adapted for operation in accordance therewith. Figure 1 illustrates a simplified form of a coking vessel with multiple feed and hot coke inlets. Figure 2 depicts a preferred coking vessel design having a conical shape for the purpose of maintaining a substantially uniform fluidizing gas rate. The feed is injected on a plurality of vertical planes spaced according to the enclosed fluidized solids volume between them. The coker, as shown, is heated by a fluidized solids type of burner.

It has now been discovered that the aforementioned difliculties in large scale fluid coking can be minimized by feeding the pitch into the reactor under special, carefully controlled conditions. More specifically it has been found that the various difliculties are due principally to excessive local concentrations of liquid feed in the fluidized bed, and to insuflicient top-to-bottom mixing. All this is further aggravated by the fact that the larger the reactor, the larger is the nozzle normally used for injecting the feed. All this results in locally reduced temperatures and unduly wet solids which tend to stick together and even become coked together before the turbulence of the bed can break up such wet agglomerates. Such a phenomenon has never been encountered in any seriousness in the most closely related commercial process, namely, in fluid catalytic cracking of gas oil, nor in small scale fluid coking operations. In the case of fluid catalytic cracking the essentially complete vaporizability apparently prevents the fluidized solids from staying wet for any appreciable time and hence turbulence throughout the fluid bed remains essentially unimpaired, despite high liquid concentrations in the vicinity of the feed inlet.

In contrast to catalytic cracking and small scale fluid coking, if all residual hydrocarbon feed is introduced at one level into a coking reactor of commercial size, quite a high local concentration of liquid is created. Specifically, for instance, feeding 5000 barrels 'of hydrocarbon per day over a single cross-section of a reactor having a diameter of 9 feet will give a feed rate of about 3.5 barrels per hours per square foot of reactor cross-section, or about 2.5 gallons per minute per square foot. This has been found somewhat excessive for satisfactory continuous fluid coking in such a comparatively tall and narrow vessel, especially with feeds contain'ing a large fraction of material unvaporizable under ticles.

coking conditions, e.g., heavy hydrocarbon feeds characterized by a Conradson carbon content of at least weight percent, and notably those having a Conradson carbon content of say 20 to 50 weight percent. Accordingly, it has been found that especially advantageous fluid coking conditions can be established in large scale operations, e.g., in operations corresponding to a feed rate of some 1,000 to 10,000 barrels or more of residual hydrocarbon per day, when this feed is introduced into the fluid bed at several consecutive levels so that the feed rate at each level is below about 5 gallons per minute per square foot of reactor cross-section, preferably between about 0.1 to 1.5 g.p.m./sq. ft. for vessels smaller than about feet in diameter, and up to about 3 g.p.m. for larger vessels ranging up to about feet in diameter. Furthermore, the successive feed levels are preferably so vertically spaced apart that approximately equal volumes of fluidized solids will exist between them. For cylindrical cokers, a preferred spacernent of the planes of injection is 1 to 2 reactor diameters. Of course, the heavier the feed and particularly the heavier its Conradson carbon content, the lower the reaction temperature, the smaller the fluidizing velocity, and the smaller the total surface of the fluidized solids per unit of reactor volume, the lower becomes the permissible feed rate at each level.

A still further improvement can be obtained by injecting not only the hydrocarbon feed at different levels, but also by introducing freshly heated solids of relatively high specific surface area into the reactor at several different levels. It is particularly preferred to return freshly burned solids into the reactor at approximately the same levels as the fresh feed so as to make the temperature distribution less dependent on back mixing. The freshly burned solids have a greater surface area and therefore greater adsorptive capacity for the liquid feed than particles of a similar size which had been in the reactor for some time and had already contacted some liquid feed. Consequently, such multiple solids injection has been found to increase utilization of the reactor to an astonishing degree, particularly in those cases where the liquid feed also is introduced at several levels.

A preferred embodiment of the invention will now be specifically described as applied to fluid coking of a vacuum reduced South Louisiana crude having an initial atmospheric boiling point of about 1000 F., a gravity of about 2 API, and a Conradson carbon content of about 30 Weight percent. However, it will be understood that the invention is broadly applicable to various other heavy hydrocarbon feeds having a gravity which may range from about l0 to API, a Conradson carbon content of about 5 to 50 weight percent, and boiling characteristic such that at least 10 or weight percent of the feed cannot be vaporized at atmospheric pressure without extensive pyrolysis. Other specific examples of such feeds are long petroleum residua having an initial boiling point above about 600 F., short residua or vacuum pitches boiling above about 1000 F., whole virgin crudes, heavy catalytic cycle oils, shale oils, various coal tar pitches, and so on.

Referring to the Figure 1, the feed is preferably preheated by conventional means, not shown, to about 400 to 800 F., e.g. to 700 F., that is, to an elevated temperature somewhat lower than actual coking temperature. The preheated feed is then pumped through line 1 at a rate of about 5000 bbl./day for introduction into fluid coking reactor 10, corresponding to a liquid feed rate of about 0.5 weight of feed per hour per Weight of fluidized solids present in the reactor. The reactor is a cylindrical vessel about 9 feet wide and about 75 feet high containing finely divided fluidized coke par- The solids may have a diameter of about 20 to 500 or 1000 microns, mostly about 80 to 300 microns.

These solids are maintainedin the form of a turbulent reactor.

fluidized mass having an apparent density of about 10 to 60 lbs/cu. ft., e.g. 40 lbs./cu. ft. and having an upper level 11 about 60 feet above the bottom of the Above level 11 is a dilute vapor phase containing only a comparatively small amount of entrained solids. Fluidization of the solids is obtained by the upflowing hydrocarbon vapors formed by the coking of the feed and also by an inert fluidizing gas such as superheated steam which is usually introduced into the bottom of reactor 10 through line 5. Conveniently the bottom part of reactor 10 may be restricted to form a well 6 wherein circulating solids may be stripped of volatilizable hydrocarbons with the aid of the aforementioned inert gas stream 5. The addition of such extraneous gas to the reactor may amount to about 0.5 to 10 weight percent based on hydrocarbon feed, 2 weight percent being a convenient value. The addition rate of this extraneous gas is desirably adjusted so as to provide a total superficial upward gas velocity of about 0.5 to 6 ft./sec., throughout the reactor. Gas velocities of about 1 to 3 ft./sec. are generally preferred, it being understood that the gas velocity tends to increase at progressively higher levels in the reactor due to the evolution of increasing amounts of hydrocarbon vapor by coking of the heavy feed.

The fluidized bed is maintained at a coking temperature of about 800 to 1200 F., preferably at about 950 F. where a distillate suitable for catalytic cracking is to be the principal desired product. Higher temperatures may be used if petrochemicals such as ethylene or aromatics are the principal desired products. The pressure in the top part of reactor 10 is usually essentially atmospheric, e.g. about 10 p.s.i.g., though higher pressures up to about p.s.i.g. as well as subatmospheric pressures may be used similarly if special considerations warrant this. Of course, the pressure at the bottom of the reactor is considerably higher than at the top, due to the pseudo-hydrostatic head exerted by the bed of fluidized solids.

In accordance with the present invention the hot feed in line 1 is introduced into the fluid bed in reactor 10 in equal portions through a plurality of feed nozzles 2, 3, and 4 located at three different levels separated from each other by a vertical distance of about 15 feet. It will be understood, of course, that the feed may be introduced at more levels than the three shown, and in certain circumstances only two feed levels may be suflicient, depending principally on the relation of the feed rate to reactor cross-section. In efiect, injecting the feed as a plurality of streams at different levels simulates the treatment of such individual streams in separate reactors having the same cross-section as reactor 10 but having a height corresponding to the distance between two adjoining feed levels only. The distribution of feed on the solids as well as the uniformity of other conditions has been found to be far better in such comparatively shallow reactors than in a deep reactor of the over-all size of reactor 10 but provided with feed injection at a single level.

The hydrocarbon vapors liberated in the fluid coking zone as well as any injected steam pass up through the fluidized bed level 11, entraining some solids and forming a dilute vapor phase having a density of about 0.01 to 1 lb./cu. ft., depending on the gas velocity, solid particle size and other well-known factors. In order to recover the entrained solids from the vapors, the latter are preferably passed through a cyclone 14 or other equivalent means adapted for separating entrained solids from gases. The separated solids then may be returned to the fluidized bed through a dip pipe 15. The more or less dust free vapors then pass overhead through line 16 for further treatment as desired. For instance, the product vapors may be fractionated and the resulting gas oil fraction catalytically cracked to form gasoline in a manner wellknown by itself, or other conventional processes may be employed depending on the final product desired. As an example, such coking of vacuum residua may produce about to 20 weight percent of coke, 7 to 12 weight percent of C and lighter gases, about 15 to 25 volume percent of a C /430 gasoline fraction, about 45 to 65 volume percent of a gas oil fraction boiling from 430 to 1015 F., and 0 to about 25 volume percent of a residual fraction. Particular figures will, of course, vary from case to case depending on the nature of the feed, specific reaction condition, the degree to which the heavy residue is recycled, etc.

As the hydrocarbon feed is coked in vessel 10 it undergoes an endothermic reaction which cracks it into lighter hydrocarbon vapors as well as a solid carbonaceous residue or coke. This coke deposits in film-like layers on the finely divided fluidized particles, causing a continuous growth in particle size. Consequently, both to maintain the solids in a properly fluidizable size range and to supply the heat of coking, some of the solid particles are continuously withdrawn from the reactor 10 through standpipe 19, preferably after stripping in aforementioned well 6. The stripped coke is then passed to a suitable heater Where it is heated to a temperature higher than the reaction temperature in coking vessel 10. This heating also tends to increase the surface area of the circulating coke by more completely converting the fresh coke produced in the process. Furthermore, additional surface area may be obtained by activating the withdrawn coke with superheated steam in any well-known manner.

A convenient way of obtaining the heat of reaction involves partially burning the withdrawn coke and returning the unburned portion to the coking zone. For instance, hot coke withdrawn through standpipe 19 may be mixed with an oxygen-containing gas such as air introduced through line 21. The resulting suspension may then be passed upwardly through a burner 20. In burner 20 the mixture of air and coke is preferably maintained as a dense turbulent fluidized bed similar to that present in vessel 10, so as to allow suflicient residence time for the combustion to proceed to the desired extent. For instance, about 15 to weight percent of the coke produced in the process may thus be consumed. The hot solid combustion residue is withdrawn from the burner through line 22, being entrained in the hot flue gases. These gases are then preferably separated from the hot solids by passage through a separating means such as cyclone 23, the gases being led away through line 24 while the separated hot solids are returned to the coking vessel through standpipe 25. A portion of the separated coke, preferably after appropriate cooling, is also desirably withdrawn through line 29 for passage to a grinder, not shown, so as to supply the required amount of seed coke for return to the coking vessel. Any net surplus of coke may also be recovered at this point as product. Alternatively, product coke and coke to the grinder may be withdrawn directly from the coking vessel or the stripper prior to passage through the burner.

Of course it will be understood that any convenient means other than the illustrated upfloW-type burner may be employed for heating the circulating solids. For instance, a bottom draw-01f may be used on the fluid burner whereby the hot solids are withdrawn directly from the fluid bed in the bottom part of the burner, instead of all solids being carried overhead in the flue gas. Likewise, instead of burning the solids in dense fluid phase, the combustion may be allowed to take place while the solids pass in the form of a dilute suspension in air through a narrow transfer line of suitable length, all of which is well known by itself. Furthermore, instead of supplying the heat of coking by partial combustion of the coke product, an extraneous fuel such as torch oil or fuel gas may be used as a source of heat, and more coke may then be recovered as product. In such an instance the required heat may be transferred to the circu- 6 lating process solids either by direct contact with the combustion gases or by indirect heat transfer.

In accordance with the present invention a special advantage is obtained when the reheated coke is returned to the coking vessel at a plurality of levels rather than at the customary single level. Specifically, instead of returning all of the reheated coke through standpipe 25, the coke may be introduced into the coking vessel 10 in approximately equal portions through a plurality of lines 25, 26 and 27, these lines preferably discharging their burden near the fresh feed jets issuing from the respective feed nozzles. In this manner, the high, narrow reactor 10 is more truly converted into a plurality of stacked reactors having a relatively small ratio of height to diameter, and thus the benefits inherent in the present invention are further enhanced. It will be understood that feed nozzles other than those shown in the drawing may be used. For instance, the feed injectors may be virtually flush with the inside reactor wall and may deliver the feed into the fluidized bed by atomization with steam, nitrogen or compressed hydrocarbon gas. Where only one such individual feed jet is used at each level, it is particularly advantageous that consecutive jets be located alternately on opposite sides of the reactor so as to assure uniform feed distribution.

Whether the hot solids are returned to the reactor at a plurality of levels or at a single one, when operating the coking vessel at 800 to 1200 F., eg at 900 F., it is desirable to heat the coke in the heater to a temperature at least about F. higher than coking temperature, heater outlet temperatures, of about 1200 to 1400 F., e.g. 1300" F., being particularly preferred. The rate of returning these hot solids will of course depend on the temperature difference between coking vessel and heater, and also on-other factors such as the preheat temperature of the feed.

It should be understood that the fluidized solids bed need not be composed of pure carbon or coke particles. Sand, quartz, spent catalyst, or the like are just as satisfactory in some applications. When such inerts are used, the carbon will be deposited on the particles in the coking vessel and consumed in the combustion zone. If desired, the coking can be so controlled that only enough carbon is deposited on the particles to supply heat for the reaction.

Figure 2 of the appended drawings illustrates another, preferred, design of a fluid coking vessel. The vessel 50 has a narrow stream stripping section at the bottom. Above this there is a conical section containing the main pyrolytic zone. The vessel is conically shaped so that the velocity of the uprising gases will remain substantially uniform despite the fact that volatilization of the feed creates additional volumes of gases. Above the pseudo-liquid level 59 of the fluid bed, the vessel necks down so that the velocity of the uprising gases will increase. In this manner, a small amount of solid particle entrainment will occur and the entrained particles will scour attendant surfaces to remove coke deposits, if any. This reactor design is more fully described in co-pending application entitled, Fluid Coking of Heavy Hydrocarbons and Apparatus Therefor, Serial No. 375,088, filed August 19, 1953, by Pfeifler et al.

Referring to Figure 2, the heated feed enters the process through manifold 51. It is sprayed into the fluidized bed by a plurality of nozzles 56 at a multiplicity of points both circumferentially and vertically. Any type of nozzle which will obtain fine dispersion of the feed without requiring excessive amounts of dispersion gas may be used. The feed enters the nozzles from the manifold by lines 52, 53, 54 and 55.

The vertical spacement of the planes of the nozzles is determined to a large extent by the volume of fluidized solids contained in the vessel between the planes. The horizontal arrangement is controlled to a large extent by the permissive feed rate per square foot of vessel area at each plane. The volume of fluidized solids necessary between planes is related to the rate at which feed is added. This is often expressed as pounds per hour per pound of fluidized solids, w./hr./w. The rate will be set by feed stock quality, feed pre-heat, operating temperature, fluidized solids characteristics and like factors. Generally, the limit for feed rate is in the range of about 0.1 to 3 w./hr./w. The corresponding volume relationship is 0.007 to 0.5 ftfi/lb. of feed per hour. It has been demonstrated that a feed rate of about 2 g.p.m. per square foot of reactor cross-section atthe plane of injection gives good performance.

The volatile hydrocarbon vapors formed by the pyrolysis pass upwardly past the pseudo-liquid level 59 of the fluid bed to cyclone separators 57. Entrained particles are removed from the vapors in the separators and returned to the bed by lines 58. The product vapors then pass overhead by line 60 to further processing such as fractionation (not shown). Steam is admitted to the coker by line 63 to fluidize the bed and to strip the coke particles of hydrocarbons prior to the particles transfer to the burner.

The excess coke produced in the process along with large size unfluidizable particles is removed by line 61 as product. A portion of the fluid bed is continuously withdrawn by line 62 and transferred to the burner 64. Bafiles 65 prevent large size particles from entering line 62. A transporting gas, e.g. steam, is supplied at a plurality of points to line 62 by lines 66. The solids in line 62 are discharged into the burner via pipe 67.

Air or a free oxygen-containing gas is admitted to the burner 64 by line 68. This air fluidizes the solid particles in the burner and supports partial combustion of the carbon-containing solids. In this manner, the fluidized solids in the burner are maintained at a temperature of about 1300" F. Baffle 69 aids the distribution of the incoming air.

The products of combustion pass upwardly to cyclones 70 where the entrained solids are removed and returned by lines 71 to the bed. The solids free flue gas is removed from the burner by line 72.

Heated coke particles at the temperature of the burner bed are continuously withdrawn by standpipe 73. These particles pass downwardly, through pipe 74 and are engaged by transporting steam supplied by lines 75 The heated solids then flow upwardly to the reactor bed. In general, about to pounds of hot solids are introduced into the reactor per pound of fresh feed.

The scope and spirit of the invention for which patent protection is sought is particularly pointed out and distinctly claimed in the following claims. a a

What is claimed is:

1. An improved hydrocarbon oil fluid coking process wherein excessive local concentrations of feed and bogging of the fluidized bed are prevented which comprises maintaining an upwardly diverging dense turbulent bed of fluidized coke particles having a size in the range of to 1000 microns in a coking zone at a coking temperature in the range of 800 to 1200 F., maintaining 'said fluidized coke particles as such by injecting a fluidizing gas into the lower portion of said coking zone in an amount in the range of 0.5 to 10 weight percent on oil feed sufficient to maintain a fluidizing gas velocity in the range of 0.5 to 6 feet per second, injecting a liquid hydrocarbon residual oil feed having a Conradson carbon content over 5 weight percent and boiling above 600" F. into said bed as a multiplicity of streams at a 7 gallons per minute per square foot of reactor cross-section at any one of said vertically spaced levels, any two of said vertically spaced levels enclosing a volume of said dense turbulent bed in the range of 0.007 to 0.5 cubic foot per pound of said residual oil injected per hour at one of the vertically spaced levels defining said volume, removing said hydrocarbon vapors overhead, recovering entrained solids therefrom, circulating a portion of said dense turbulent bed through an external heating zone and returning heated solids at a temperature at least F. above said coking temperature from said heating zone to said coking Zone to maintain said coking temperature.

2. A hydrocarbon oil fluid coking process for converting heavy residual oils which comprises maintaining hot particulate solids in the form of a conical dense fluidized mass, injecting a heavy residual oil into said dense mass at a plurality of vertically spaced levels, the total feed rate of said heavy residual oil being 0.1 to 3 weights/hr./ weight of particulate solids, and the volumes of said conical dense fluidized mass between said vertically spaced levels being maintained within the limits of 0.007 to 0.5 cu. ft./lb. of residual oil injected per hour at any one vertical level, whereby bogging of the fluidized mass is prevented and maximum feed rates are achieved.

3. The process of claim 2 wherein said heavy residual oil is injected at a plurality of horizontal points at each of said vertical levels at a rate within the limits of 0.1 to 3 gals./minute/sq. ft. of reactor cross-section at each of said vertical levels.

References Cited in the file of this patent UNITED STATES PATENTS 2,362,270 Hemminger Nov. 7, 1944 2,621,118 Cyr et al. Dec. 9, 1952 2,661,324 Leifer Dec. 1, 1953 2,709,676 Krebs May 31, 1955 2,714,116 Teichmann et al. July 26, 1955 2,731,400 Jahnig et al. Jan. 17, 1956 2,731,508 Jahnig et al. Jan. 17, 1956 2,736,687 Burnside et a1 Feb. 28, 1956 2,786,801 McKinley Mar. 26, 1957 

2. A HYDROCARBON OIL FLUID COKING PROCESS FOR CONVERTING HEAVY RESIDUAL OIL WHICH COMPRISES MAINTAINING HOT PARTICULATE SOLIDS IN THE FORM OF A CONICAL DENSE FLUIDIZED MASS, INJECTING A HEAVY RESIDUAL OIL INTO SAID DENSE MASS AT A PLURALITY OF VERTICALLY SPACED LEVELS, THE TOTAL FEED RATE OF SAID HEAVY RESIDUAL OIL BEING 0.1 TO 3 WEIGHTS/HR./ WEIGHT OF PARTICULATE SOLIDS AND THE VOLUMES OF SAID CONICAL DENSE FLUIDIZED MASS BETWEEN SAID VERTICALLY SPACED LEVELS BEING MAINTAINED WITHIN LIMITS OF 0.0007 TO 0.5 CU. FT./LB. OF RESIDUAL OIL INJECTED PER HOUR AT ANY ONE VERTICAL LEVEL, WHEREBY BOGGING OF THE FLUIDIZED MASS IS PREVENTED AND MAXIMUM FEED RATES ARE ACHIEVED. 